68 COMPARATIVE MORPHOLOGY OF FUNGI 



In contrast to the Ancylistaceae, a new structure has arisen, especially 

 in the female gametangium. Its content is no longer changed into a 

 single multinucleate egg, but, as in the primitive gametangium, it is 

 split into uninucleate daughter cells, here called oospheres. These may 

 not be considered homologous to true female gametes, however, for their 

 nuclei only represent the remaining privileged sexual nuclei. Morpho- 

 logically the eggs are coenocytic; functionally, however, the female 

 gametes have recovered atavistically to a certain degree their earlier 

 individuality; to be sure, they no longer swarm, but each acquires a male 

 nucleus for itself through a special branch of the fertilization tube. The 

 process is the same as in Olpidium in which (if one considers them heterog- 

 amous) several sexual acts occur between the gametes of two gametangia 

 and several zygotes result. In the Saprolegniaceae a number of sexual 

 acts between the two gametes of two gametangia occur and many 

 zygotes (oospores) result; only the male gametes are no longer recogniz- 

 able as individuals and the female gametes always remain in the game- 

 tangia; thus the sexual acts are shifted back to the female gametangia 

 where the zygotes remain enclosed. 



After maturity of the oospores, the oogonia remain connected with 

 the mycelium until it disintegrates ; much later they, too, degenerate so 

 that the oospores are liberated and germinate. Usually after a rest of 

 2 to 5 months, germination takes place with a germ tube where meiosis 

 occurs. According to the nutrient content of the environment, it ends 

 in a sporangium after a short time or develops to a mycelium. The rest 

 period does not seem indispensable in all species; thus, in S. mixta, it may 

 be shortened to 8 to 10 days by placing the oospores in pure water at 

 23 to 25°. 



Achlya americana (Trow, 1899), A. debaryana (Trow, 1904), A. poly- 

 andra (Miicke, 1908) and Plectospira myriandra (Drechsler, 1927) agree 

 essentially with Saprolegnia monoica in reproductive processes, as far as 

 they have been studied. In A. americana, Trow first observed meiosis 

 in the germination of the oospores, finding four chromosomes in the 

 nuclear figures and eight in the first division of the zygote nucleus. In 

 Aphanomyces laevis (Dangeard, 1891; Kasanovski, 1911), there is a 

 notable reduction which is reminiscent of the relationships in Myzo- 

 cytium and in the Peronosporaceae. After mitosis all the oogonial nuclei 

 degenerate except one, the future egg nucleus. The single egg results 

 from the protoplasm rounding up gradually in the interior and consuming 

 all the protoplasm contiguous to the wall. In the center of the egg is a 

 thick, deeply staining bit of protoplasm which probably corresponds to 

 the coenocentrum (coenosphere) of the Peronosporaceae. In the antheri- 

 dium, also, all nuclei but one degenerate; this, together with the proto- 

 plasm, penetrates the oogonium through a copulation tube and fuses 



